1. Field of Invention
The present invention relates to a toner for developing an electrostatic charge image used for an electrophotographic method, an electrostatic recording method, electrostatic printing method etc., a developing agent for electrostatic charge image using the toner, and an image formation method using the developing agent.
2. Description of Related Art
As a fixing method for toner for developing an electrostatic charge image, a heating roll method is widely employed. In recent years, in order to speed up copying machines and to decrease energy consumption, using a heating roll having a smaller size in order to increase thermal efficiency, and fixing with a thin film have been proposed. However, since the heating roll is contacted with melted toner in the heating roll method, the toner is transferred to the surface of the roll, and re-transferred to a transferred material such as paper, polluting it. As a result, hot offset tends to occur.
A method of controlling viscoelasticity at the time of melting the toner by enlarging the molecular weight dispersion of a binding resin of the toner so as to avoid the occurrence of hot offset, and a method of decreasing adhesive force with a heating roll and film by adding a releasing agent such as wax in a toner, have been proposed. However, by these methods, the dispersion property of wax cannot be controlled sufficiently. When the releasing agent is a polyolefin wax, polyolefin is not easily dispersed since it only slightly dissolves in toner. As a result, a big domain of polyolefin is formed in a polyester resin, the toner is ground in the domain area at the time of grinding, and the polyolefin is easily exposed on the surface of the toner or liberated. In particular, when a magnetic developing agent is used, the polyolefin pollutes the toner carrying member (sleeve), providing for non-uniform toner carrying, decreasing the ability of the toner to provide charge and decreasing the image density. In order to maintain lower prices, in the case of, for example, small type machines using a magnetic one-component developing agent, the mechanism for cleaning a photosensitive member is often kept simple. Particularly in these less expensive machines, the liberated polyolefin wax pollutes the photosensitive body causing image faults (line). Thus the offset resistance of toner is not sufficient, and there are secondary faults such as with regard to powder flowability and a transfer of wax component to a photosensitive body and a carrier. These problems remain to be resolved.
A technique of satisfying low temperature fixing property, grindability and blocking resistance by using, as a binding resin for the toner, a polyester resin whose molecular weight dispersion is enlarged by incorporating cross-linking structure, is proposed in Japanese patent Publication No. 7-86699-B, No. 7-86700-B and No. 7-86701-B. However, even if a releasing agent such as a low molecular weight polypropylene is finely dispersed in a polyester resin in an effort to provide sufficient offset resistance, the compatibility of wax such as a low molecular weight polypropylene with a polyester resin having a relatively strong polarity is often insufficient. As a result, it is difficult to disperse the polypropylene in the polyester resin uniformly.
In order to resolve these problems, a technique of improving the wax dispersion property by improving compatibility of the polyester resin and the wax by using oxidative-type polyolefin wax having a polar group in the terminal position of a molecule is proposed in Japanese Patent Publication No. 7-244402-A. With this method, although the dispersion property of the wax is improved, the powder flowability and heat resistance of the toner are deteriorated. A technique of using aliphatic petroleum resin as a releasing agent is proposed in Japanese Patent Publication No. 7-199534-A. However, the same problems of deterioration of the powder flowability and heat resistance of the toner result. In addition, since the polyester resin itself is tough, grindability is limited, thus providing for lower productivity when a small size toner is needed to attain the high image quality of copied image.
In order to resolve the problems of grindability and heat resistance, the use of an aromatic petroleum resin is proposed in Japanese Patent Publication No. 4-257868-A, and the use of a hydrogenated petroleum resin is proposed in Japanese Patent Publication No. 8-278658-A. Although the use of these resins can improve grindability, they have no effect on improving the dispersion property of a releasing agent. In addition, these resins deteriorate the charging property of the toner.